1. Field of the Invention
The present invention relates to a control system in a hard disk drive. In particular, the present invention relates to controlling the positions of transducer heads during self-writing of servo data.
2. Related Technology
FIGS. 1 and 2 show typical components of a hard disk drive. The disk drive, generally identified by reference number 10, includes a base 12 and magnetic disks 14. The magnetic disks 14 are rotated relative to the base by a spindle motor (not shown) that is mounted to the base 12. An actuator arm assembly supports a transducer head 24 near the surface of each disk. Each transducer head 24 includes a read element for reading data and signals from the disk surface and a write element for writing data and signals to the disk surface.
Each actuator arm assembly includes a first stage 16 and a second stage 18. The first stages 16 are mounted to an axle 20 and are driven by a primary actuator 22 such as a voice coil motor or linear motor to radially position the actuator arm assemblies with respect to the disk surfaces. The first stages are fixed with respect to one another and move together. The second stages 18 are joined to corresponding first stages 16 in a manner that allows the second stages 18 to move with respect to the first stages 16 through planes parallel to the surfaces of their corresponding disks, such as by pivoting or sliding with respect to the first stages 16. The articulation of the second stages 18 with respect to the first stages 16 may be provided by a journal bearing, a flexible interconnection, or any other joining structure that allows the second stages 18 to move with respect to the first stages 16. Each second stage is moved by a microactuator (not shown). Various types of microactuators may be employed, including a piezoelectric actuator, an electromagnetic actuator, and an electrostatic actuator. Examples of microactuators are provided in U.S. Pat. No. 5,189,578 and U.S. Pat. No. 5,867,347.
The primary actuators 22 and microactuators position the transducer heads 24 with respect to tracks on the disk surfaces. The operation of the primary actuator 22 and microactuators is controlled by a servo system based on servo data read from the disk surface. The servo data typically includes track number data fields that are used for coarse positioning during track seeking and settling operations and sector number data fields that provide circumferential location information within the track. The servo data further includes servo bursts that are embedded within the user data tracks. The servo bursts generate an analog signal that is representative of the lateral position of the transducer head read element relative to the center line of the track. The signals generated by the servo bursts are used by the servo controller to generate control signals that are applied to the primary actuator and microactuators to optimize the track following operation. Examples of servo burst patterns and their use in controlling the position of a transducer head are provided in U.S. Pat. No. 5,301,072, U.S. Pat. No. 5,771,131, U.S. Pat. No. 6,266,205, U.S. Pat. No. 6,369,974, U.S. Pat. No. 6,452,990, U.S. Pat. No. 6,614,608, U.S. Pat. No. 6,643,082, and U.S. Pat. No. 6,721,124. The track seeking operation typically employs only the coarse actuator 22 but in some instances may also employ the microactuators. The microactuators are typically used for settling the transducer head 24 position immediately following the seek operation, and for controlling the position of the transducer head 24 during the track following operation.
FIG. 3 shows a diagram of control circuitry and related elements within a typical hard disk drive. As described above, a primary actuator 34 such as a voice coil motor controls the position of the actuator arm assembly. As further described above, the hard disk drive includes transducer heads 30 that are also moveable by microactuators 32. In the illustration of FIG. 3, the transducers 30 and microactuators 32 are labeled such that elements with the same numbers (e.g. transducers 1a and 1b) correspond to the same disk, while elements with the same letters (e.g. transducers 1a and 2a) correspond to disk surfaces having the same orientation, i.e. upper surfaces or lower surfaces.
The hard disk drive also includes read/write circuitry 36 that processes data and signals that are read from or written to the disks by the transducers 30. User data read from or to be written to the disks may be communicated with a host device through an interface 38. Servo data and signals read from the disks may be supplied to a servo controller 40. The servo controller 40 includes circuitry for performing signal processing such as discrete Fourier transformation and spectral analysis on a position error signal generated from servo burst signals obtained from the transducer heads to generate primary actuator and microactuator control signals to control the positions of the transducers 30. A variety of implementations for providing primary actuator and microactuator control may be utilized, including a parallel loop implementation, a master-slave loop implementation, a dual feedback loop implementation, and a master-slave with decoupling implementation. The servo controller supplies the same control signal to all of the microactuators 32. The arrows associated with the microactuators 32 in FIG. 3 indicate that all of the microactuators have the same wiring polarity. For purposes of this document, microactuators are considered to have the same wiring polarity if they move in the same direction in response to a signal supplied by the servo controller 40.
A disk drive controller 42 coordinates the operation of the elements of the hard disk drive including the interface 32, the servo controller 34, and the read/write circuit 36. The disk drive controller 42 also identifies the tracks that the transducers 30 are to seek or follow and supplies that information to the servo controller 40.
Servo data is written to the disk surfaces during manufacturing. The servo data may be written prior to assembly of the hard disk drive by a servo track writer in a clean room environment using laser interferometry to precisely position the transducer heads as the servo data is written. However this process is time consuming and cost intensive, and so several alternatives have been developed. In one alternative, a master pattern is written to one surface of a reference disk using a servo track writer, and a hard disk drive is then assembled using that disk and one or more additional blank disks. The master pattern may be servo data or a different pattern from which position information may be derived to enable the writing of servo data. After assembly, the master pattern on the reference disk is used as a reference pattern to facilitate the self-writing of servo data (also called “self-servo writing”) to all disk surfaces. The self-servo writing process may be performed in accordance with a self-servo writing program that is executed by the hard disk drive controller and its associated components. Examples of this type of process are provided in U.S. Pat. No. 5,012,363, U.S. Pat. No. 6,519,107, U.S. Pat. No. 6,600,620, U.S. Pat. No. 6,631,046, and U.S. Pat. No. 6,714,376. In another alternative, a reference pattern is imprinted on a master disk surface by means of magnetic printing before assembly. After assembly, the reference pattern is used to provide position information in a self-servo writing process that writes servo data to all disk surfaces. Examples of this type of process are provided in U.S. Pat. No. 6,304,407. U.S. Pat. No. 6,704,156 and U.S. Pat. No. 6,738,205. In a third alternative, a pure or self-propagating self-servo writing process is performed in a hard disk drive that is assembled from blank disks containing no reference patterns. Initially a reference pattern is self-written to one of the disk surfaces using, for example, an inner or outer crash stop as an initial point of reference. Subsequently the reference pattern is used to provide position information in a self-servo writing process that writes servo data to all disk surfaces. Examples of this type of process are provided in U.S. Pat. No. 5,668,679, U.S. Pat. No. 6,771,443, U.S. Pat. No. 6,798,610, and U.S. Pat. No. 6,819,518.